PO3 RPO should not appear on a C10-30 or K10-20 Cheyenne Super SPID as it was equipment included in the
trim level (not to be confused with RPOs for included equipment on package trucks that
were listed on SPIDs - like 72 Highlander YG# trucks). If you've seen PO3 and YE9 on a SPID together, it would have been an anomaly.
The other, much less commonly seen RPO than the PO1 full wheel cover that you could see on a C10 Super SPID was PA1 - the full wheel cover that was included on 72 C10 Highlander YG# package trucks.
I have, however, seen some wackiness on Oshawa SPIDs - their Z84 nomenclature/description was sometimes "Cheyenne Super" - in which case PO3 (if ordered) did appear on the SPID (because the truck is truly only a Cheyenne trim level if the RPO is Z84, regardless of the description). So this can cause some confusion.
There were no factory trim rings in this era. If the SPID had PO1 on it and the truck had caps/rings, they were added at some point, and the rings wouldn't be era-correct standard or optional equipment. If I had a nickel for every original owner that swore up and down "this was how it was when I bought it..." I could buy a Cheyenne Super
